In conventional art, a doctor blade is used to remove a paste, constituted by alumina powder and a binding agent mixed in a solvent, from a surface of a reverse gravure roll, which reverse gravure roll is used to form a heat-resistant layer of a separator for a lithium ion secondary battery by applying the paste to a resin original sheet serving as a resin part of the separator. The doctor blade disclosed in Patent Literature 1 has an edge section made of metal.